Use the exclude-paths option in the dependabot.yml update entry to list directories Dependabot should skip, e.g. the experiments folder. This applies per update entry, so set it on each ecosystem block that scans near the excluded paths. It keeps the noise PRs away without moving the experiments out of the repo or disabling Dependabot for the directories you do care about.

Context: Stack Overflow #65275433 (accepted answer, 37 votes): the asker has an /experiments directory full of one-off package.json files they never intend to maintain, but Dependabot keeps opening PRs for them. The accepted answer notes this was impossible for years and is now supported via configuration.